I think that it sounds wonderful. Tell him your schedule after he arrives. Rules...before. Plans...after, so that he cannot balk.
You might want to buy crafting supplies or flowers to make a centerpiece to bring for M's sister. Or shop for a special hostess gift.
Movies at home are okay, but might leave time and privacy for a fight or disagreement.
Maybe, you could buy plants out together to plant when he is gone. Plan how to landscape an area. Have him help you pick out paint chips for a room. Go to the public library or a bookstore. I do not know your area. Look in your paper for local plays or events. Go to thrift shops to find fun items. Who can find the best thing for $5 or less? Shop with him to pick out his gifts in advance for the holidays. Or, have M take him out to buy YOU gifts for the holidays...even better. Tunics??? Have fun!
I am proud of my warrior sister.